The present invention relates generally to an arrangement for open-end friction spinning having two rollers that are arranged next to one another, are drivable in the same rotational direction and form a wedge-shaped gap used for yarn forming. The rollers each have a perforated shell and suction inserts arranged therein. The inserts are each provided with a suction slot facing the wedge-shaped gap and extending essentially along in the direction of the wedge-shaped gap. Also included is a feeding device that feeds individual fibers to the wedge-shaped gap in a scatter zone, a withdrawal device that withdraws the forming yarn in a longitudinal direction relative to the wedge-shaped gap from the scatter zone and a connected processing zone of the wedge-shaped gap.
It was found that by means of arrangements of this type, as are are disclosed, for example, in DE-OS 33 21 228 and AT-PS 339 778, yarns of a satisfactory quality can be spun. This is particularly true when, in accordance with the disclosure of to DE-OS 33 21 228, it is provided that the friction effect in the area of the scatter zone is adapted to the forming yarn in such a way that the lowest friction effect exists in the area of the yarn tip and the highest friction effect exists in the area of the end of the scatter zone located in yarn withdrawal direction. However, in the case of these arrangements, the yarn breakage number is unsatisfactory.
An arrangement is also known (DE-OS 30 08 622) in which the scatter zone extends practically over the whole axial length of the two rollers. The suction slots of the suction inserts are inclined with respect to a plane placed through the roller axes in such a way that the opening of the suction slots enlarges gradually in the withdrawal direction of the yarn. In this case, it is also provided that the width of the suction slot (in the circumferential direction of the suction insert) of the roller rotating into the wedge shaped gap is larger than the width of the suction slot of the suction insert of the roller rotating out of the wedge-shaped gap.
An objective of the present invention is the provision of an arrangement of the initially mentioned type wherein the number of yarn breakages is reduced.
This objective and other objectives of the present invention are achieved by providing the suction slot of the suction insert of the roller rotating into the wedge-shaped gap with a greater length than the suction slot of the suction insert of the roller rotating out of the wedge-shaped gap.
By means of an arrangement of this type, longer running periods are possible with fewer yarn breakages. It is believed that the reason for this improvement is that the spinning tension is reduced to a suitable extent without any significant impairment of the friction effect.
In a further development of the invention, it is provided that the suction slot of the suction insert of the roller rotating out of the wedge-shaped gap extends essentially only over the processing zone. By means of this development, particularly favorable results are obtained with respect to a low frequency of yarn breakages and a high yarn quality. In this case, the suction air flow directed into the roller rotating out of the wedge-shaped gap is essentially effective only in the processing zone.
In a further development of the invention, it is provided that the suction insert of the roller rotating out of the wedge-shaped gap, in the area of the scatter zone, is equipped with at least one air inlet opening aimed at the wedge-shaped gap, and that the shell of this roller is perforated in this area. As a result, individual fibers are effectively prevented from being caught at the roller rotating into the wedge-shaped gap and rotating together with it. In this case, it is sufficient for the at least one air inlet opening to have an inlet cross-section that is only a fraction of the inlet cross-section of the suction slot of this suction insert.
In a further development of the invention, it is provided that the suction slot of the suction insert of the roller rotating into the wedge-shaped gap, in the area of the scatter zone, has a section that - looking in circumferential direction of this roller - exhibits a greater separation from the wedge-shaped gap than the section located in the area of the processing zone. This section, that is larger opposite the rotating direction, has the result that a softer twist is introduced in the area of the yarn tip, while at the same time the inclination of the yarn tip to form curls is reduced. By the placing of this section of the suction slot away from the wedge-shaped gap, the suction air flow is displaced somewhat out of the wedge-shaped gap.
In a further development of the invention, it is provided that the suction inset of the roller rotating into the wedge-shaped gap, at least in the area of the scatter zone, is equipped with an adjusting device by means of which the free cross-section of the section or of the sections of the suction slot of the suction insert can be adjusted. As a result, it is possible to precisely dose the suction pull and thus also the tension affecting the yarn tip and, if necessary, also adapt it to a different fiber material to be spun.
In a further development of the invention, it is provided that the feeding device contains a fiber feeding duct that has a mouth extending in a slot-shaped way in the direction of the wedge-shaped gap. The transport direction of the fiber feeding duct has a component that is directed against the yarn withdrawal direction. This construction that is disclosed by itself in DE-OS 30 08 622, results in an improved yarn quality especially in connection with the arrangement and alignment of the suction slots of the suction inserts according to the present invention.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings, which show for purposes of illustration only, an embodiment constructed in accordance with the present invention.